An informal skateboarding competition turned disruptive and confrontational Tuesday night at Dolores Park in San Francisco when police rushed in to break up the show and a crowd of nearly 400 faced off with them.

The tension lasted for more than an hour as skaters shouted and threw objects at the cops, one officer was injured and two police cruisers were damaged. The standoff shut down Dolores Street between 18th and 20th streets until around 9 p.m., when officers felt they had the situation under control.

The trouble flared around 7 p.m., when first one, then two skateboarders wiped out so badly during the downhill street-riding competition on Dolores Street that ambulances were called to take the victims to a hospital. Some skaters said the first wipeout occurred when a police officer tried to stop one of the competitors as he rolled down the hill.

However, Police Officer Robert Rueca said the cop and the skater actually just collided. The officer was taken to a hospital to be treated for non-life threatening injuries, Rueca said. The skateboarder in the collision, a man, and a female skateboarder who wiped out later, were also taken to a hospital, Rueca said.

By then, the impromptu contest that had begun earlier in the evening had swelled to include hundreds of participants and onlookers lined up along the street to watch skateboarders whisk down the pavement, and residents were calling in to complain of disruption and an inability to use all of the street, said police spokeswoman Officer Grace Gatpandan.

As dozens of officers rolled up, scores of skateboarders and onlookers scattered and hundreds of others massed to face off with police, Gatpandan said. The damage to the cruisers happened sometime during the confrontation, she said.

“The officers were just trying to keep them safe when this all happened,” Gatpandan said.

The competition is an annual event called “hill bombing,” and several skaters said they didn’t intend anyone to get hurt — but were proud that they mustered enough of a crowd to turn the street into their own territory for a time. Most skaters wore no helmets as they zipped downhill.

“We literally shut down Dolores Street,” said one 22-year-old skater from San Francisco, who gave his name only as Pete. “They (police) were doing their job. That doesn’t mean we always agree with it.

“It got very very serious very fast. Then the cops got involved and the skaters got mad.”